Pursuit watts/cda?

swampy1970 said:

Yes I am.

It was a laugh. A good two hours, dropped on the approach to the hill on cantelow and a 300watt time trial up pleasants valley, putah creek and back down to Timms to get back on. Rinse and repeat.

Climbing the back of Monitor Pass after 180 miles on the Alta alpina seemed easy...

That was a frustrating race. I made it up the final climb within 10 meters of the leaders and descended behind a guy who put us 50 meters behind turning onto Pleasants Valley. Three of us chased flat out the last handful of miles to no avail. I am in awe of how 10 meters at the top of a climb turns into a minute and a half by the finish line.

I'm with you....the long distance slogs are a piece of cake compared to this. All of my agony on Carson for the DR was a drop in the bucket to the pain of the chase......

Which category did you race?

Alex Simmons said:

BTW - I'm heading up there again in Oct, riding the Granfondo again and then will be traveling a bit for a couple of weeks.

I am toying with idea suggested to me of running a practical clinic on using power meter for aero testing while there. Go through the options/theory (at a lay level), head out for some data collection, then back for the analysis. More about learning how to go through the process, as usually it takes a few times to get the process down pat.

Sounds interesting.

teebone said:

That was a frustrating race. I made it up the final climb within 10 meters of the leaders and descended behind a guy who put us 50 meters behind turning onto Pleasants Valley. Three of us chased flat out the last handful of miles to no avail. I am in awe of how 10 meters at the top of a climb turns into a minute and a half by the finish line.

I'm with you....the long distance slogs are a piece of cake compared to this. All of my agony on Carson for the DR was a drop in the bucket to the pain of the chase......

Which category did you race?

I guess in keeping with this thread, it'd be apt to describe Pleasants Valley Rd as a wind tunnel, what with those line of trees down the side. 😉 Those little gaps will grow like that in a near instant. Add a bit of wind and a nice rolling road and it a recipe for fun.

Vaguely trying to keep this on topic... You doing the time trial next Sunday? If you see a guy riding a funky looking steel tubed TT bike around the flatlands of Elmira with an aero potty on his head at the of the week then that'll be me.

swampy1970 said:

what do you think the best method of testing cda is in an area that's windy but nearly pan flat?

You've probably heard of "power meter as altimeter." I've also been working on "power meter as anemometer." Basically, you need to do a single zero wind ride to set a baseline condition in a repeatable configuration. That will allow you to establish the virtual elevation profile which, if your power meter is right and you measured the air density properly and if you held your position exactly, ought to be the true elevation.

Then all subsequent rides done when it's windy (doesn't have to be the same day, but the wind should be steady in speed and direction) include a baseline configuration ride. Subtracting off the "true" elevation profile will allow you to determine the virtual wind. If the wind really is steady in speed and direction you can then correct your test runs for it.

Seems to work okay. You do need that baseline zero wind run.

Thanks for that. I'd be interesting in reading more details about that if you have a link to share.

Measuring air density... I guess I'll have to refer to the reading from Travis AFB and Vacaville muni airport, which are ~3 miles away (in opposite directions), for that.

Looking at past wind history for my area it looks like this the baseline would have to be a 4am to 6am test. Not really too sure if I want to attach a 'coal miners light' to the front of my helmet to read the PT.

Jono L said:

Heck, you don't want to do it at any time:eek:

Been there, done that 21 y ago. The good news is that all I carry with me are bad memories and an ugly scar.

RChung said:

You've probably heard of "power meter as altimeter." I've also been working on "power meter as anemometer."

Use of powermeter as an anemometer (from 8/2008):

Wattage | Google Groups

swampy1970 said:

Thanks for that. I'd be interesting in reading more details about that if you have a link to share.

Measuring air density... I guess I'll have to refer to the reading from Travis AFB and Vacaville muni airport, which are ~3 miles away (in opposite directions), for that.

Looking at past wind history for my area it looks like this the baseline would have to be a 4am to 6am test. Not really too sure if I want to attach a 'coal miners light' to the front of my helmet to read the PT.

Well, remember that you don't need to use a flat venue. VE lets you use non-flat venues so you can look for somewhere that's protected from the wind. I suppose you could even use a segment of Mix Canyon.

acoggan said:

Wattage | Google Groups

Yeah, I think the idea has come up several times. I considered discussing it in my first analysis of Dede Demet's Montreal WC file in 2003 -- but only in speculative, theoretical, form since it wasn't until way after then that I had a file that was collected under zero wind conditions.

RChung said:

Well, remember that you don't need to use a flat venue. VE lets you use non-flat venues so you can look for somewhere that's protected from the wind. I suppose you could even use a segment of Mix Canyon.

Mix is the last place I'd want an aero helmet on my head... although if you'd like to demonstrate how to climb the last half of that hill in full aero tuck I'd be willing to take the ride out. It'd be more entertaining than seeing Vaughters and Horner kill each other in the 7 mile stage back in 2003. 😉

swampy1970 said:

Mix is the last place I'd want an aero helmet on my head... although if you'd like to demonstrate how to climb the last half of that hill in full aero tuck I'd be willing to take the ride out. It'd be more entertaining than seeing Vaughters and Horner kill each other in the 7 mile stage back in 2003. 😉

I think that *would* be kinda entertaining. However, I was simply pointing out that you don't need to do this on a flat road so you can, instead, focus on finding a sheltered road no matter what its profile may be. I've done aero testing at surprisingly slow speeds up a medium-grade hill. Well, surprisingly slow because it was a nasty surprise how slow I was.

RChung said:

I think that *would* be kinda entertaining.

Yes it would. I'd have the kids come out and hand up bottles if you'd like 😉

RChung said:

However, I was simply pointing out that you don't need to do this on a flat road so you can, instead, focus on finding a sheltered road no matter what its profile may be. I've done aero testing at surprisingly slow speeds up a medium-grade hill.

Interesting.

I'd been thinking about something similar but to try to test to see at what speeds does being aero really matter on a hill.

RChung said:

Well, surprisingly slow because it was a nasty surprise how slow I was.

... you mean that there was a point in time where you didn't have recent data to reference prior to a test? :pDon't worry too much about it though, I have a 1 min power output equivalent to a hamster... a dead hamster at that. 13 years of no racing will do that to a guy.

Andy,

I see that your power profiling chart is pretty accurate. It very accurately predicts that I suck at crits and anywhere that repeated efforts under 1 minute are required.

If you could add another section to the bottom, like...

Cat 4
Cat 5
Untrained
Swampy

... then that'd be great. At least then in WKO+ I could finally see something in that part of the power profile chart. 🙂

swampy1970 said:

I'd been thinking about something similar but to try to test to see at what speeds does being aero really matter on a hill.

Well, I guess whether it "matters" depends on whether you're in a race -- but you can detect the difference in aero drag between two configurations at pretty low speed. This is a good thing because if your wind-free venue is up a hill you don't have to do trials up it at, say, 25 mph in order to detect and estimate the difference.

swampy1970 said:

Measuring air density... I guess I'll have to refer to the reading from Travis AFB and Vacaville muni airport, which are ~3 miles away (in opposite directions), for that.

Well the barometric pressure won't vary much over that distance but it's usually a good idea to have your own temperature gauge for checking local temps. If you do it regularly, then sometimes you'll notice a consistent difference between local weather station and your test location.

RChung said:

Sounds interesting.

Yeah, like I said, nothing confirmed and it might just be a handful of people in any case. It's more sorting the logistics.

You are welcome to come along of course (if I do it), could no doubt pick some holes in the process for me!

Alex Simmons said:

Yeah, like I said, nothing confirmed and it might just be a handful of people in any case. It's more sorting the logistics.

You are welcome to come along of course (if I do it), could no doubt pick some holes in the process for me!

Cool. Maybe we could figure out how much a burrito and beer affect the estimate.

RChung said:

Cool. Maybe we could figure out how much a burrito and beer affect the estimate.

I thought the claims of gaseous human propulsion were all but dismissed...
... or is this a secret weapon that's about to be unleashed on the TT world?

I would have thought that a good hot chili with beer as a catalyst would have been more apt.

:p

swampy1970 said:

I thought the claims of gaseous human propulsion were all but dismissed...
... or is this a secret weapon that's about to be unleashed on the TT world?

I would have thought that a good hot chili with beer as a catalyst would have been more apt.

:p

I ran a book to see how long before the first fart joke appeared.
I lost, it took longer than I thought.
😄

Alex Simmons said:

I ran a book to see how long before the first fart joke appeared.
I lost, it took longer than I thought.
😄

Trust me, if I wasn't for the fact I was busy planning training and doing work stuff it would have happened way, way sooner 😉

... And by chance did you happen to calculate how long it would take for the joke by using a power meter?

Alex Simmons said:

Well, wind kinda sucks for testing.

The issues are twofold:
1) Your CdA is constantly changing because yaw is constantly changing. Using Aerolab, you get a yaw-averaged CdA. It's ok, I guess, but not quite a wind tunnel.
2) Wind mucks-up virtual elevation completely anyway.

I second Alex's reply. There's not much I can do with wind right now in Aerolab.

Here's a rundown of the numerical approaches I've taken so far using VE with wind:

1) Ignore it.
Bad idea. The error on CdA is almost boundless. In fact, you can get any CdA you want, from -0.500 to +1.500 if you ignore wind. Might be a good approach if you like to brag to friends. :-)

2) Use iAero/iBike.
iAero does tend to "clean up" some Aerolab files, but not ever as much as I'd like. If your out-and-back is straight and almost perfectly aligned with the wind direction, you might get ok results. But how common is that?

The iAero has no ability to untangle yaw and airspeed. Yes, the front-facing port is yaw-sensitive, but it's also airspeed sensitive. No way to reliably untangle those yet.

3) Use a numerical "zippering" approach for out-and-backs.
Pretend that at every point in an out-and-back, the wind term is (CdA*0.5*RHO*(v-w_i)^2) going out and (CdA*0.5*RHO*(v+w_i)^2) coming back. w_i is the wind at point i.

This way, you could theoretically start from the turn-around point and "zipper" the "out" ve curve with the "back" ve curve, one point at a time. I've attached the out and back file.

Unfortunately, I've not had a lot of luck with this yet. 🙁

4) Make a wind sensor that's yaw-sensitive.
Points 1-3 have led me to what I think is the inevitable conclusion: a new sensor needs to be built. Alex has pointed it out, above.

The sensor will be ANT+ aware, and provide yaw direction, and airspeed. A printed circuit board is presently under construction.

That's it -- those are the options.

Cheers,

Andy
andyfroncioni.com